1. Field of the Invention
This invention relates to a composite substrate for a thin-film magnetic head.
2. Description of the Prior Art
An improvement in recording density and wear resistance is strongly required for a magnetic head for use in a computer, or an audio, VTR or like apparatus. A thin-film magnetic head manufactured by using IC technology is considered to best satisfy those requirements.
A thin-film magnetic head includes a substrate which is made of a soft magnetic material such as Mn-Zn or Ni-Zn ferrite or Sendust, or a non-magnetic material of high wear resistance and precision workability, for example, a ceramic material such as Al.sub.2 O.sub.3 -TiC, Al.sub.2 O.sub.3 -TiO.sub.2 or Al.sub.2 O.sub.3 -Fe.sub.2 O.sub.3. An electrically conductive substrate is necessary to be formed an insulating film on the substrate, which is non-conductive and high in mechanical strength and hardness is formed on a carefully polished substrate surface from an oxide such as Al.sub.2 O.sub.3 or SiO.sub.2 to ensure electrical insulation from two layers of a soft magnetic material, such as permalloy or Sendust are formed on the substrate and a copper, aluminum or like conductor
The insulating oxide film is formed by thin-film forming techniques, such as vacuum deposition, CVD (chemical vapor deposition) or sputtering, and has a thickness of, say, several to 50 microns. This film, however, has a rough surface, depending on the surface roughness of the substrate and the conditions under which the film has been formed. If a film of a magnetic material is formed directly on the rough surface of the insulating film, it becomes extremely inferior in film magnetic properties to a bulk material, such as a sputtering target, in a highfrequency range. The rough surface of the insulating film is, therefore, polished mechanically by, for example, a diamond powder. The surface is, however, still unsatisfactory in smoothness, and moreover, the stress created by the polishing operation remains therein. Accordingly, the film of a magnetic material formed thereon remains unsatisfactory in magnetic properties.